Here are a few UI improvements I believe would really enhance the player's experience.

1) End of game menu

Upon finishing a match, instead of exiting to the main menu, have a menu with the following options:

Exit (selected by default to retain the former behaviour)

Rematch (Play the exact same deck against the same opponent, applies to constructed & other formats)

Random rematch (Play the exact same deck against another random opponent, applies to constructed & other formats)

Edit deck (only when playing constructed obviously)

This is important because browsing through huge player/AI deck collections is time consuming (not to forget that loading times are getting out of hand on the PSP). And usually, when I create a new deck, I play with it over and over again.

2) Deck selection menu
Add the possibility to edit/create a deck from the deck selection menu.